It is common for a consumer to use shopping carts instead of hand-held basket while doing his/her-shopping in a wholesale store or a supermarket, not only because it is convenient and labor-saving, but also because it can carry more items than that of the basket in one shopping trip. Recently, along with the advance of RFID technology, the idea of attaching RFID devices to a shopping cart for facilitating the operations at the checkout counter has been proposed, and such usage of RFID technology can be found in the relating patents list as following: R,O,C, Pat. No. 588267, U.S. Pat. No. 6,179,206, U.S. Pat. No. 6,659,344, and U.S. Pat. No. 5,729,697.
Nevertheless, the PFID devices referred in the abovementioned patents are emitting radio frequency (RF) constantly for scanning inside the shopping cart and the surrounding thereof all the way with a shopper during shopping. That is, the REID devices of prior art only focus on the usages and the applications thereof, and without concerning the influence of electromagnetic wave generated thereby to human body, also without considering the power source for powering the RFID devices. In fact, it is noted that the scanning range of a RFID device is not limited inside the shopping cart where it is attached to, but can interrogate the RFID-tagged objects inside other nearby shopping carts or on the shelves as is revealed in the U.S. Pat. No. 6,659,344, moreover, there may be corners inside the shopping cart that is blind to the RFID device, which may be caused by the placing and stacking of RFIG-tagged objects in the shopping cart, as is revealed in the U.S. Pat. No. 5,729,697.
An RF electromagnetic wave or RF “field” has both an electric and a magnetic component (electric field and magnetic field), and it is often convenient to express the intensity of the RF environment at a given location in terms of units specific for each component. For example, the unit “volts per meter” (V/m) is used to measure the strength of the electric field (electric “field strength”), and the unit “amperes per meter” (A/m) is used to express the strength of the magnetic field (magnetic “field strength”). Another commonly used unit for characterizing an RF electromagnetic field is “power density.” Power density is defined as power per unit area. For example, power density can be expressed in terms of milliwatts per square centimeter (mW/cm2) or microwatts per square centimeter (μW/cm2). With respect to frequencies in the microwave range and higher, power density is usually used to express intensity. According, as specified in the FCC safety guidelines for the 800˜900 MHz range, the safe RF level is 1000 μW/cm2. Moreover, the safety regulation specified by the Directorate General of Telecommunications of Minister of Transportations and Communications of R.O.C is listed in the table hereafter.
ElectricMagneticFieldFieldPowerFrequency RangeStrengthStrengthDensityDuartion(MHz)(V/m)(A/m)(mW/cm2)(minutes)0.3–3.0 6141.63*100303–301842/f4.89/f*180/f23030–30027.50.0731.030 300–1,500——f/15003015,000–100,000——1.030*represents the equivalent plane wave power density
Imaging that as every shopping carts in a store is equipped with a device constantly radiating RF signal, each shopper in the store is conceived to receive overdosed electromagnetic wave easily, which is unhealthy and is also true for the sale persons in the store as well
Moreover, since the RFID device attached on a shopping cart will consume power, it is required to send the shopping cart to a maintenance location for charging such that the store will have to prepare a lot more shopping carts and a larger space for storing the same. Further, it is possible for a RFID device of a shopping cart to run out of power while the shopping cart is being used by a shopper, in that might cause some trouble for both the shopper and the store. It is also a consideration that the all-time-power-on RFID device is a waste of energy and is not a good idea for environmental conservation.